Crosslinkable silicone composition for the production of non-stick coatings for flexible substrates and an attachment-promoting additive contained in this composition
Crosslinkable or crosslinked silicone compositions that can be used, in particular, to form a non-stick and water-repellent coating or film for flexible substrates and in the form of natural or synthetic polymer films are provided. These compositions comprise crosslinking organopolysiloxanes bearing SiH units and unsaturated organopolysiloxanes, preferably vinyl organopolysiloxanes, capable of reacting with the crosslinker by addition reaction, in the presence of platinum in order to form the non-stick crosslinked coating on the flexible substrate, and at least one crosslinking and attachment-promoting additive X. These compositions are advantageously free of solvent and can be crosslinked instantaneously into a non-stick and/or water-repellent coating for a flexible substrate.
1. A silicone composition A comprising a silicone base B capable of crosslinking or curing by polyaddition and comprising at least one additive X which is a linear organopolysiloxane comprising siloxyl units (I.1) to (I.3) having the formulae below:
Y
a
Z
b
1
SiO
4
-
(
a
+
b
)
2
(
I
.1
)
Z
3
2
SiO
1
2
(
I
.2
)
H
d
Z
e
3
SiO
4
-
(
d
+
e
)
2
(
I
.3
)
and not comprising units of formula (I.4):
Z 2 2 SiO 2/2 (I.4)
in which
a=1 and b=1 or 2,
d=1 and e=1,
Y is
the symbols Z 1 , Z 2 and Z 3 , which may be identical or different, are chosen from the group formed by alkyl groups containing from 1 to 8 carbon atoms and aryl groups containing from 6 to 12 carbon atoms,
with the following conditions:
the additive X comprises, per molecule, at least two siloxyl units (I.1) bearing Y, at least three siloxyl units (I.3) bearing hydrosiloxyl groups and a total number N of siloxyl units of between 7 and 30,
the additive X has a content of siloxyl units (I.1) of greater than or equal to 0.2 mol per 100 g of additive X, and
the additive X does not comprise any functional group selected from the group consisting of an alkoxy, vinyl, hydroxyl, and methacryloxy functional groups.
2. The silicone composition A as claimed in claim 1 , wherein the additive X has a content of siloxyl units (I.1) of greater than or equal to 0.2 mol per 100 g of additive X and a content of siloxyl units (I.3) of greater than or equal to 0.3 mol per 100 g of additive X.
3. The silicone composition A as claimed in claim 1 , wherein the additive X has a number N1 of siloxyl units (I.1) and a number N3 of siloxyl units (I.3) which satisfy the following conditions:
2≤N1≤10, and
3≤N3≤20.
4. The silicone composition A as claimed in claim 1 , wherein the additive X has a total number N of siloxyl units of between 7 and 25, limits inclusive.
5. The silicone composition A as claimed in claim 1 , wherein the content of additive X is between 0.3% and 10% by weight relative to the total weight of the composition A.
6. The silicone composition A as claimed in claim 1 , wherein the silicone base B comprises:
(A) at least one alkenylated organopolysiloxane E comprising at least two siloxyl units (I.5) having the formula below:
W
a
Z
b
SiO
-
4
-
(
a
+
b
)
2
(
I
.5
)
in which:
a=1 or 2, b=0, 1 or 2, and a+b=1, 2 or 3;
W independently represents an alkenyl group, and
Z independently represents a monovalent hydrocarbon-based group containing from 1 to 30 carbon atoms, and
(B) at least one polyaddition catalyst F.
7. The silicone composition A as claimed in claim 1 , wherein the amounts of constituents are such that a [≡SiH]/[≡SiAlkenyl] molar ratio is between 1 and 7, wherein:
[≡SiH]=total number of moles of siloxyl units comprising a hydrogen atom bonded to the silicon within the silicone composition A, and
[≡SiAlkenyl]=total number of moles of siloxyl units comprising an alkenyl radical bonded to the silicon within the silicone composition A.
8. The silicone composition A as claimed in claim 1 , wherein the additive X has a dynamic viscosity at 25° C. of between 10 and 700 mPa·s.